Self-ejecting electric plug

ABSTRACT

The plug includes a plunger normally spring retracted between the prongs and a chamber containing thermally expansible material and an electric heater which is the plug cord circuit, a remote switch closure energizing the heater to expand the material against the plunger to drive it outwardly and eject the plug from the receptacle.

United States Patent lnventor Lee M. Harris [56] References Cited A I Ngg rg UNITED STATES PATENTS ff A 1968 2,548,708 4/1951 Dickey P2,597,890 5/1952 Monk atented Sept. 28, 1971 A 2,688,734 9/1954 Wellingssignee Product Design & Manufacturing Corp. 3 168 805 2/1965 Flwilloughby Ohio eury 2,612,419 9/1952 Reynolds.... 3,084,901 4/1963Thorbum Primary Examiner-Richard E. Moore Attorney-Oberlin, Maky,Donnelly & Renner SELF -EJECTING ELECTRIC PLUG sclmmsz'nmwing ABSTRACT:The plug includes a plunger normally spring U.S. Cl 339/45, retractedbetween the prongs and a chamber containing ther- 60/25 mally expansiblematerial and an electric heater which is the Int. Cl H0lr 13/62 plugcord circuit, a remote switch closure energizing the Field of Search339/45; heater to expand the material against the plunger to drive itoutwardly and eject the plug from the receptacle.

SELF- UECTING ELECTRIC PLUG This invention relates to an electric plugwhich can eject itself from a receptacle for self-disconnect action.

The copending application of John T. Venaleck, Ser. No. 689,663, filedDec. 11, 1967 and now Pat No. 3,475,715 issued Oct. 28, 1969, disclosesa plug assembly on this order in which the ejection is under the controlof a solenoid included in the circuit which is energized by connectionof the plug in the receptacle. More particularly, this assemblycomprises a plunger between the contact prongs which is normally biasedoutwardly by a spring and mechanically latched within the plug whenpushed in by the insertion of the plug in the receptacle. The solenoid,when its circuit is completed by closure of a switch, withdraws thelatch, thereby freeing the plunger for outward drive by its spring andhence the ejection of the plug from the receptacle.

One primary area of interest for this plug has been in electric cordsfor portable appliances used in the home, with the vacuum cleaner beinga prime example, and it has been found that the variation inreceptacles, especially throughout older homes, is even greater than wasexpected, with the result that the plug for this application required afairly heavy spring force for reliable ejection. Increasing the springforce of course requires proportionately more pressure by the housewifein the insertion of the plug in the receptacle, with the latchnecessarily stronger, the solenoid larger, and the overall sizeincreased.

it is a principal object of the present invention to provide such a plugwith an improved ejector mechanism having appreciably greater capacitywithout the noted shortcomings of the solenoid plug form.

Another object is to provide an improved self-ejecting plug which isinexpensive to produce and relatively trouble free by virtue ofsimplicity of its design and operating mode.

Other objects and advantages of the present invention will becomeapparent as the following description proceeds.

To the accomplishment of the foregoing and related ends the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawing setting forth in detail a certain illustrativeembodiment of the invention, this being indicative, however, of but oneof the various ways in which the principle of the invention may beemployed.

In said annexed drawing:

FIG. 1 is a perspective view of a new self-ejecting electric plug inaccordance with the present improvements;

FIG. 2 is a longitudinal sectional view of the plug as indicated by theline 2-2 in FIG. 1; and

FIG. 3 is an electrical schematic of a plug and appliance combination.

Referring now to the drawing in detail, the plug comprises first andsecond body parts and 11, which are preferably made of rigid plastic.The part 10 is generally annular, thereby defining a bore 12, with aradial stop flange 13 at the outer end of the bore and an annular relief14 in the inner end face for purposes to be described.

The part 11 is in the nature of an end cap having a cylindrical recess15 on the same axis as the bore 12, with a slightly larger insidediameter as shown. The outer or open end of the part 11 abuts the innerend of the part 10, with the two having the same outside diameter, andthe end face of the former has a groove 16 opposed to the annular relief14 in the end face of the latter.

An elastic diaphragm 17, made for example of rubber, is arranged as awall separating the recess 15 from the adjoining bore 12 and sealing thejoint between the parts 10 and 11 by having a peripheral bead l8sealingly gripped in the groove 16 and relief 14. The diaphragmpreferably has a fold 19 which it normally assumes and which permitsready distension of the diaphragm outwardly into the bore 12.

The recess contains a quantity of thermally expansible and contractablematerial 20 and a schematically shown electric heating coil H operativewhen energized to expand such material and thereby exert an outwardforce at the diaphragm l7.

Such force is applied through the diaphragm to a plunger 21 in the bore12, also made of a rigid plastic, having a flange 22 at its inner end. Areturn spring 23 extends from this plunger flange to the stop flange 13at the outer end of the bore 12 and serves normally to hold the plungerin the relatively retracted condition shown. Two metal prongs 24, 25 areattached to the outer face of the body part 10 by bolts 26, 27 whichextend completely through this part and also through the part 1] at therear of which they receive electric wire terminals 28, 29 and nuts 30,31. Accordingly, the bolts serve also to unite the body parts 10 and 11and electrically connect the prongs 24, 25 respectively to the terminals28, 29. The plunger is between the prongs, and two wires 32, 33 extendfrom the terminals 28, 29. As shown in the schematic of FIG. 3, one endof the heating coil H is connected to wire 32, while the other continuesas a third wire 34. The plug assembly is encased within an insulativecover 35, for example, of rubber molded thereabout, and the wires 32, 33and 34 extend through an insulative cord body 36 to the appliance orother device served by the cord.

In the H6. 3 schematic, the circle 37 represents an electric applianceand dashed line 38 the division between the plug circuit, above theline, and the cord and appliance circuit. The latter includes an on-ofiswitch 39 and additionally a pushbutton switch 40 connected betweenwires 33 and 34, so that the heating coil in the plug can selectively beenergized by closure of the pushbutton conveniently at the appliance.

When a housewife operating the appliance wishes to disconnect the plugfrom the circuit, she need only close the heater switch 40, with theresulting heating of the thennally expansive material 20 in the plugalmost immediately effective to force the plunger 21 outwardly againstthe return spring force for automatic ejection of the plug from thereceptacle. Such material is selected to provide quick response withinsubstantially normal plug size and it has been found that Freon, ahalogenated hydrocarbon containing a fluorine atom, is very satisfactoryin this respect and also in recycling. This inert, dielectric liquidwill vaporize art about 200 F., and that part of the liquid contacted byand proximate to the heater in the plug can be almost immediately heatedto this temperature sufiiciently to develop ejection force with arelatively small resistance element at normal energization; For example,a plunger force well over the 15 lbs. which appears reliable forejection from household sockets, has been developed in less than 1second with a heater of about 470 watts at l 15 volts.

When the plug is ejected, the circuit for the heater in the same is alsoautomatically disabled along with the appliance or other cord connecteddevice, the expansion material as quickly contracts and the returnspring retracts the plunger to its normal nonobstructive position. Thepower output is substantial and more than adequate readily to effectdisconnection of even a tightly held plug.

it will also be apparent that the number and character of the componentspermit economic manufacture with high efiiciency and reliability. Whilethe heating coil has been shown schematically for convenience ofillustration, it can in fact be a simple wire coil of sufficient heatingcapacity relative to the fluid or material used to perform with thedesired quick response.

While the plug part of the plug-receptacle combination is preferably theactuated part in the described application, it will be appreciatedgenerally that such an automatic disconnect can also be realizedcomparably by incorporating the ejecting assembly in the receptacle,with the plunger in this case normally retracted between the socketcontacts and driven outwardly against the plug to eject the latter.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described, provided thefeatures stated in any of the following claims or the equivalent of suchbe employed.

I, therefore, particularly point out and distinctly claim as myinvention:

1. A thermally actuated device for converting electrical energy rapidlyto mechanical energy by volume and pressure increase due to a liquid togas phase change of a working fluid, comprising body means, adistensible member in sealed engagement with said body means fonning afluid chamber therewith, said distensible member including an annularfold therein projecting into said fluid chamber and adapted forunfolding upon an increase of pressure in said fluid chamber, saiddistensible member having a central portion supported by said annularfold adapted for substantially linear movement away from and toward saidbody means, an inert dielectric fluorinated hydrocarbon liquid fillingsaid fluid chamber when said distensible member is in a foldedcondition, electrical resistance heating means supported in said bodymeans, being disposed in said fluid chamber and completely submerged insaid liquid for heating that portion of said liquid in contact therewithto vaporization temperature, thereby to raise the pressure in said fluidchamber and cause movement of said distensible member and furthercomprising means for confining said distensible member for suchsubstantially linear movement, said confining means being exterior ofsaid body means and rigidly connected thereto.

2. A thermally actuated device as set forth in claim 1 furthercomprising a plunger supported for linear movement in said confiningmeans, said plunger being in abutment with said central portion of saiddistensible member, and a spring in engagement with said plunger forurging same against said distensible member.

3. A thermally actuated device as set forth in claim 2 wherein saiddistensible member is a rubber diaphragm adapted for distension withoutstretching, by rolling along said annular fold therein, therebyproviding substantially no resistance to movement of said centralportion.

4. A thermally actuated device as set forth in claim 3 wherein said bodymeans comprises a rigid cup and said diaphragm is secured at the mouthof said cup, said annular fold being fully received within said cup andadapted for unfolding exteriorly thereof to provide linear movement ofsaid central portion greater than the depth of said cup.

5. .A thermally actuated device as set forth in claim 4 wherein saidconfining means comprises a cylindrical member rigidly secured to saidcup and adapted for support of said plunger and said spring.

1. A thermally actuated device for converting electrical energy rapidlyto mechanical energy by volume and pressure increase due to a liquid togas phase change of a working fluid, comprising body means, adistensible member in sealed engagement with said body means forming afluid chamber therewith, said distensible member including an annularfold therein projecting into said fluid chamber and adapted forunfolding upon an increase of pressure in said fluid chamber, saiddistensible member having a central portion supported by said annularfold adapted for substantially linear movement away from and toward saidbody means, an inert dielectric fluorinated hydrocarbon liquid fillingsaid fluid chamber when said distensible member is in a foldedcondition, electrical resistance heating means supported in said bodymeans, being disposed in said fluid chamber and completely submerged insaid liquid for heating that portion of said liquid in contact therewithto vaporization temperature, thereby to raise the pressure in said fluidchamber and cause movement of said distensible member and furthercomprising means for confining said distensible member for suchsubstantially linear movement, said confining means being exterior ofsaid body means and rigidly connected thereto.
 2. A thermally actuateddevice as set forth in claim 1 further comprising a plunger supportedfor linear movement in said confining means, said plunger being inabutment with said central portion of said distensible member, and aspring in engagement with said plunger for urging same against saiddistensible member.
 3. A thermally actuated device as set forth in claim2 wherein said distensible member is a rubber diaphragm adapted fordistension without stretching, by rolling along said annular foldtherein, thereby providing substantially no resistance to movement ofsaid central portion.
 4. A thermally actuated device as set forth inclaim 3 wherein said body means comprises a rigid cup and said diaphragmis secured at the mouth of said cup, said annular fold being fullyreceived within said cup and adapted for unfolding exteriorly thereof toprovide linear movement of said central portion greater than the depthof said cup.
 5. A thermally actuated device as set forth in claim 4wherein said confining means comprises a cylindrical member rigidlysecured to said cup and adapted for support of said plunger and saidspring.